1. Field of Invention
The present invention relates to circuits and methods for adjusting a system clock in response to low voltage detection; particularly, it relates to circuits and methods which suspend or slow down, but do not immediately reset, an essential clock inside of an integrated circuit when a low voltage condition is detected, and a corresponding low voltage reset circuit.
2. Description of Related Art
An electronic circuit often requires a low voltage reset (LVR) circuit which is capable of generating a reset signal to initialize internal settings of the electronic circuit during system power on process. The electronic circuit may further include another LVR circuit which may be the same as or different from the previous LVR circuit, to reset the electronic circuit when a low voltage condition occurs during system operation, so as to avoid damages caused by circuit malfunction.
Typically, a specification of normal operation voltage range is defined in product design and development. When it is detected that the operation voltage is lower than the lower voltage limit, the LVR circuit will be triggered. However for safety, this lower voltage limit is usually designed to be higher than required. For example, assuming that the standard operation voltage is 1.8V, it is typically designed to generate a reset signal when the supplied voltage is lower than 1.6V. However, such arrangement may unnecessarily reset the system due to an occasional voltage surge, such that the product can not pass product test wherein the conditions are usually set stricter. In the foregoing example, it often happens that the circuit is unnecessarily reset under ESD test, because voltages lower than 1.6 V often occur. Therefore, it is preferred if the threshold for low voltage reset can be set to a lower level to avoid triggering unnecessary reset. However, this is in conflict with the design specification which guarantees a minimum operation voltage, that is, there is a potential risk of circuit malfunction if the lower voltage limit is set lower.
In view of the foregoing drawback, the present invention is proposed as a solution to it.